Process for gelatines extraction and chromium salts recovery from tanned hides and skins shavings

ABSTRACT

The present invention refers to a continuous process for gelatines production and chromium recovery from tanned hides and skins shaving, containing trivalent chromium. The claimed process consists in an acid hydrolysis followed by separations of the various products, wherefrom three major components are obtained: gelatine from collagen, tanning chromium salt, used for hides and skins tanning, and the hydrolysing agent. The gelatines obtained can be used as adhesives in various industrial sectors, i.e. from the industry of abrasives to the paper and cardboard industry, to bookbinding, to the industry of dyes and plasters, to the production of matches. The chromium salts obtained can be recovered and reused in the tanning industry; the hydrolysing agent may be recycled.

FIELD OF THE INVENTION

The present invention refers to a process for gelatine extraction andchromium salts separation from tanned hides and skins, with recovery ofthe hydrolysing agent.

TECHNICAL NOTE

The environmental impacts of hides and skins tanning are mostsignificant since the process produces large amounts of hardlydisposable wastes and uses highly polluting heavy metals, such aschromium. Therefore, the disposal of by-products of the tannery industryis a real problem. The methods of disposal adopted so far are thefollowing: waste disposal in authorised landfills, non-differentiatedwaste incineration in bulk, and waste conversion—though in very lowamounts—into nitrogen fertiliser. However, said methods do not solve theproblem, but make it more serious: in fact, the wastes from the tanneryindustry contain approx. 3% chromium, which, though trivalent, is aheavy metal and tends to accumulate. Therefore, when said wastes aredisposed of in landfills or are used for the production of nitrogenfertiliser, they cause serious soil pollution problems. Incineration isnot advisable at all as it brings about the formation—by hightemperature oxidation—of highly toxic hexavalent chromium and othercombustion by-products, also in the gas phase, which are polluting andtoxic to varying degrees.

On the other hand, as suggested by the attempts made to dispose ofwastes through the so-called “leather torrefaction”—which gives nitrogenfertiliser—most by-products, after adequate treatments, may be of higheconomic value from the recycling viewpoint. It is common knowledge thatby-products of the tannery industry can give technical-grade gelatinesas well as chromium, which, if recovered appropriately, may be reused inhides and skins tanning. In fact, most of said by-products consist ofcollagen-derived protein materials, which can yield different gelatineshaving a wide range of industrial application. Except for the foodstuffor pharmaceutical industries, for which the use of products from tanneryis forbidden, technical-grade gelatines are widely used especially asadhesives in many other industrial sectors, e.g. in the industry of dyesand plasters, of matches and abrasives, textiles, paper and cardboard,and bookbinding.

Traditionally, the most widely used process for technical-gradegelatines production from by-products derived from hides and skinssplitting, consists in practice as example a treatment with 15% limewashand in the washing with running water, followed by lime residuesneutralisation with acids and gelatines extraction in water at atemperature of 80° to 100° C. However, this process is characterised bya very high water consumption (up to 80 m3/hr) as well as by theproduction of poor-quality technical-grade gelatines. Furthermore, thesector of technical-grade gelatine production has now to face adifficult situation, i.e. the scarce availability of startingby-products, mostly due to the present trend to locate said productionsin developing countries. However, the technical-grade gelatines producedin developing countries not always comply with the technicalspecifications requested by product users.

Instead, tanned hides and skins shaving is sufficiently, if notabundantly, available in industrialised countries, where other problemsarise in connection with shaving disposal and by-products recovery forrecycling (collagen gelatine and chromium). To this end, severalprocesses for gelatines production from low-chromium-content collagenhave been developed: they are mostly based on alkaline hydrolysis withhot strong alkalis, gelatine extraction, chromium insolubilisation,followed by successive separations. In other processes, alkalinehydrolysis is preceded by chromium removal from the hides and skinsshaving with acid chemical agents capable of binding trivalent chromiumand by the separation of same by precipitation. In still furtherprocesses, hydrolysis is followed by the oxidation of the trivalentchromium residue to hexavalent chromium and by the separation of same.Said processes for the obtainment of low-chromium content gelatines,based on treatments with alkaline reagents for collagen hydrolysis andchromium separation, are multi-stage and therefore hardly applicable tothe industrial sector. However, alkaline treatments give low-qualitygelatines and bring about the production of ammonia by the amidic groupdegradation.

It is, therefore, a major object to develop a process, easily applicableto industrial plants, which, starting from tanned hides and skinsshaving containing Cr(III), might allow—through few steps—the obtainmentof choice collagen gelatines in high yields as well as chromium saltsthat may be recovered and reused in industrial plants. Consequently, theproblem arising from their disposal would be minimised. It is a furtherobject to develop an industrially efficient production process having noenvironmental impact, which, therefore, may envisage a complete reuse ofits by-products (wastewaters and hydrolysing agent), and does notgenerate polluting gas emissions.

SUMMARY

A surprisingly advantageous process according to the objects of thepresent invention has been developed by the Applicant. Theprocess—involving few steps and no alkaline treatment—gives a choiceproduct (gelatines) with good Bloom mechanical resistance, which,therefore, may be used for industrial purposes, and allows the recovery,from tanned hides and skins shaving, of chromium, which may be reused inthe tanning industry. From an industrial point of view, the claimedprocess also allows the recovery of its by-products (hydrolysing agentand water), and from an environmental point of view it is compatiblewith environmental impact requirements. Hence it complies with theobjects of the present invention.

Therefore, it is an object of the present invention to provide a processcharacterised by acid hydrolysis of tanned hides and skins shaving,containing chromium(III), at a pressure below the atmospheric and atrelatively low temperatures.

The process for gelatines production and chromium salts recovery, objectof the present invention is characterised at least by the followingsteps:

-   -   a) organic acid hydrolysis of tanned hides and skins shaving        products at temperatures to 100° C.;    -   b) extraction of the raw gelatine in solution obtained after        hydrolysis by filtration with recycling of non-hydrolysed        products, if any, to hydrolysis;    -   c) gelatine and chromium salts separation by desalination over        ion exchange resins.

Further objects of the present invention are i) recovery of the acidhydrolysing agent and water for recycling and ii) total chromiumrecovery after desalination by ion resins selective regeneration.

DETAILED DESCRIPTION OF THE INVENTION

As shown in the flow diagram of FIG. 1, the process for g latinesproduction and chromium salts recovery from tanned hides and skinsshaving, forming the object of the present invention, is continuous typeand consists in the following steps:

-   -   a) organic acid hydrolysis of tanned hides and skins shaving        products at temperatures to 100° C.;    -   b) dilution with water of the material resulting from the first        hydrolysis;    -   c) extraction of the raw gelatine in solution obtained after        hydrolysis by mechanical filtration with recycling to hydrolysis        of non-hydrolysed products, if any;    -   d) gelatine separation from chromium salts and clarification of        the same by desalination carried out by filtration through ion        exchange resins;    -   e) concentration, cooling and drying of the resulting gelatine        and water recycling;    -   f) concentration of the chromium salts obtained by ion exchange        filters standard regeneration, by evaporation in vacuo with        recovery of chromium salts and of water to be recycled.

As reported in the Summary, the essential production stepscharacterising the whole process are: acid hydrolysis in an aqueousmedium of tanned hides and skins shaving products; raw gelatineextraction by filtration of the hydrolysate in solution; gelatineseparation by desalination over ion exchange resins with gelatineclarification and chromium separation.

A detailed description of the production steps indicated in the flowdiagram of FIG. 1 is given hereinbelow.

Acid Hydrolysis

Tanned hides and skins shaving products having an average moisturecontent of approximately 55%, which otherwise would be disposed of, aresent to plant storage areas, wherefrom they are conveyed and fed toreaction tanks, provided with products weighing means. On the basis ofthe amount of products loaded, through a preset programme, an electroniccontrol system calculates the amount of reagents to be fed (water andacids). To favour hydrolysis, the mass may be maintained under continuedstirring.

The quantity of acids is predetermin d at 10 to 80% wt/wt in respect ofthe w ight Of shaving as it is, with an averag moisture content ofapprox. 55%. Water is fed at room temperature in a water weight ratioranging from 4 to 10 times the weight of shaving as it is, having anaverage moisture content of approximately 55%.

The hydrolysing agents preferably used for acid hydrolysis are organicacids selected from the group consisting of monocarboxylic,polycarboxylic, hydroxy acids, such as for example formic, lactic,citric, EDTA, tartaric acids and equivalent acids, the salts andmixtures thereof. Optionally, the organic acids, both salified and asmixtures thereof, may be added with mineral acids, such as for examplesulphuric, phosphoric and equivalent acids in an amount of 5 to 20% inrespect of the shaving mass.

The mass in the tank is heated to a temperature up to 100° C. and thetime of residence under said temperature conditions is from 0.5 to 30hours. By way of example, the mass may be heated with steam at apressure of 0.5 to 1 bar.

The temperature and the time of residence under the selected temperatureconditions influence the hydrolysis of the protein material and,consequently, the quali- and quantitative yield of the gelatineproduced. To a higher temperature and longer time corresponds a gelatinein higher yields, but of poorer quality, measured as mechanicalresistance index (Bloom's parameter). It follows that the processphysical parameters are to be fixed on the basis of the type of gelatineto be produced.

Continuous mass mixing by blade or anchor stirrer favours the hydrolysiskinetics and increases the yield.

Raw Gelatine Dilution and Extraction by Filtration

Once acid hydrolysis has been performed, the mass in the reaction tankis added with the water necessary for the other steps. The hydrolysedprotein fraction, which consists of raw gelatine, is separated from thesolid mass fraction consisting of non-hydrolysed shaving products, byfiltration with mechanical filtering means, such as for example,centrifugal separators, drum filters, bag filters, filter press,rotational separators and equivalent means. The solid mass is defined asunreacted solid residue. The protein fraction hydrolysed in solution,which contains raw gelatine, is conveyed to the successive steps, whilethe solid fraction is recycled to hydrolysis. The hydrolysis/filtrationsequence may be repeated on the chromium solid residue to extract thegreatest possible, if not the whole amount of gelatine. The gelatinequalitative yields are constant independently of the increase in numberof the xtraction cycles.

Gelatine Separation by Desalination

The raw gelatine solution obtained by mechanical filtration contains thehydrolysing agent, chromium salts and impurities, such as ashes, inamounts exceeding the allowable limits provided for by the technicalspecifications of the product for industrial use.

The raw gelatine solution is subjected to desalination to simultaneouslyfree the solution from water, acid hydrolysing agents and chromium saltresidues and to abate ashes, without significant protein substanceslosses. The purification takes place by filtration through ion, cationand anion or mixed-bed exchange resins, selective for trivalentchromium. Resin filters are periodically regenerated to extract thecaptured chromium salts. The regeneration solution is then recycled tothe separated chromium salts concentration step.

Concentration, Cooling and Drying

The resulting gelatine solution is fed to a multiple-effect evaporatorand then coooled and dried, e.g. in air dryers.

Chromium Salts Concentration

The chromium salts solution, containing trivalent chromium salts,obtained by resins regeneration of the desalination step, isconcentrated by evaporation preferably in vacuo, to give a concentrate,utilised by salcrome manufacturers for tanning, and water which isrecycled.

With a view to improving the process yields and efficiency, the claimedprocess for gelatines and chromium salts production may optionallyinclude, after acid hydrolysis (step a) and after raw gelatinefiltration (step c), the following steps:

-   -   gelatine separation from chromium salts and clarification by        dialysis across membranes;    -   chromium salts separation by diafiltration through membranes        with separation from the hydrolysing agent of the first step and        recycling of the same.

The above optional steps allow the obtainment of gelatine of higherquality and the recovery of chromium-free hydrolysing agent, which maybe recycled again. The gelatine solutions obtained in the first dialysismay be sent to desalination or directly concentrated and dried aspreviously described.

As shown in detail in the flow diagram of FIG. 2, the process formingthe object of the present invention, is continuous type and includes thefollowing steps:

-   -   a) organic acid hydrolysis of tanned hides and skins shaving        products at temperatures to 100° C.;    -   b) dilution with water of the product obtained from the first        hydrolysis;    -   c) extraction of raw gelatine in solution obtained after        hydrolysis by mechanical filtration and recycling of        non-hydrolysed products, if any, to hydrolysis;    -   d) gelatine separation by dialysis across selective membranes        for gelatine clarification and separation from chromium salts;    -   e) gelatine desalination by filtration of the chromium residue        through resins;    -   f) concentration, cooling and drying of the gelatine separated        and water recycling;    -   g) chromium separation by diafiltration through membranes        selective for chromium salts with separation from the        hydrolysing agent of the first step;    -   h) concentration of the hydrolysing agent over selective        membranes with recovery of the same and of water to be recycled;    -   i) concentration of chromium salts obtained by diafiltration and        ion exchange filters regeneration, by evaporation in vacuo with        recovery of chromium salts and water to be recycled.

The essential production steps characterising the whole process are:acid hydrolysis of tanned hides and skins shaving products; raw gelatineextraction by filtration of the hydrolysate in solution; gelatineseparation from chromium and clarification by dialysis, diafiltration ofthe solution containing chromium salts.

The optional steps included in the flow diagram of FIG. 2 are describedin detail hereinbelow. The basic steps are as described above.

Gelatine Separation by Dialysis

The raw gelatine solution obtained by mechanical filtration may beoptionally subjected to dialysis before desalination. By portionwisewater addition, dialysis allows the simultaneous removal of acidhydrolysing agents and chromium salts from the water solution and theabatement of ashes, without significant protein losses. The filteringmeans used for dialysis are porous membran s with molecular sieves of1,000 to 30,000 dalton, which retain protein molecules of approx. 50,000dalton and do not retain low-ionic-charge molecules, such as chromiumsalts and acids. The acid solution recovered from dialysis Is sent tothe recovery of the hydrolysing solution and chromium salts.

Chromium Salts Separation by Diafiltration

The solutions containing the chromium salts and hydrolysing agentrecovered from dialysis are diafiltered through selective membranes, toseparate chromium salts from the hydrolysing agent. Diafiltration usesfiltering means with porous membranes with molecular sieves of 200 to500 dalton, which retain the bi-trivalent ion species and do not retainlow-ionic-charge molecules, such as the hydrolysing agent. The twofractions are recovered after an appropriate concentration. Thehydrolysing agent is recovered up to 70%.

Hydrolysing Agent Concentration

The hydrolysing agent is recovered and recycled to hydrolysis afterconcentration, which may be performed with reverse osmosis membranes orwith evaporators in vacuo. The water recovered is recycled.

Chromium Salts Concentration

The chromium salts solutions, which contain trivalent chromium, obtainedby diafiltration and resins washings of the desalination step, areconcentrated by evaporation in vacuo, as previously described. Theconcentrate obtained is utilised by salcrome manufacturers for tanning.Water is recycled.

With a view to efficiently recovering—from an industrialstandpoint—mainly the chromium separated and secondarily the hydrolysingagent, the claimed process, after desalination optionally includes aparticular type of ion exchange regeneration, meant for:

-   -   decreasing the consumption of reagents used in ion exchange        filters regeneration;    -   producing a more concentrated chromium salts solution that does        not require a further concentration, thereby reducing the        volumes to be concentrated and effecting a saving in energy.

As shown in the flow diagram of FIG. 3, the claimed process iscontinuous typ and includes the following steps:

-   -   a) organic acid hydrolysis of tanned hides and skins shaving        products at temperatures to 100° C.;    -   b) dilution with water of the material obtained by the first        hydrolysis;    -   c) extraction of the raw gelatine in solution obtained after        hydrolysis by mechanical filtration with recycling of        non-hydrolysed products, if any, to hydrolysis;    -   d) gelatine desalination by filtration of the chromium residue        through resins;    -   e) selective regeneration of ion exchange filters;    -   f) concentration, cooling and drying of the gelatine separated        and water recycling.

The optional steps included in the flow diagram of FIG. 3 are describedin detail hereinbelow. The basic steps are as described above.

Selective Regeneration of Ion Exchange Filters

Whenever ion exchange filters lose their ability to retain salts, theymust be regenerated by means of adequately diluted acid and alkalineregenerants and of successive washings. The technique adopted hereconsists in the separation of three regeneration phases, denominatedhead, core, and tail, where:

-   -   the head is poor in regenerant and chromium salts;    -   the core is poor in regenerant, but is rich in chromium salts,        and forms the concentrated phase;    -   the tail is rich in regenerant and poor in chromium salts.

Head and tail are combined and, by fresh regenerant make up,reconstitute the regenerating solution for the next regenerating cycles.

The core consists of a solution with a chromium content of 2 to 4% bywt., which does not need any further concentration.

The consumption of regenerant (both alkaline and acid) is therebyreduced by approx. 50%, while the volume of exhaust wash waters, whichstill contain chromium salts and, therefore, must be concentrated, Isreduced by approx. 70%. The continuous process for gelatines productionand the complete recovery of chromium salts, as well as of thehydrolysing agent and water, which consists of all steps previouslydescribed, also includes the following steps, as reported in the flowdiagram of FIG. 4:

-   -   a) organic acid hydrolysis of tanned hides and skins shaving        products at temperatures to 100° C.;    -   b) dilution with water of the material obtained by the first        hydrolysis;    -   c) extraction of the raw gelatine in solution obtained after        hydrolysis by mechanical filtration and recycling to hydrolysis        of non-hydrolysed products, if any;    -   d) gelatine separation by dialysis across selective membranes        for gelatine clarification and separation of the same from        chromium salts;    -   e) chromium separation by diafiltration through membranes        selective for chromium salts with separation from the        hydrolysing agent of the first step;    -   f) concentration of the hydrolysing agent over selective        membranes with recovery of the same and of water to be recycled;    -   g) gelatine desalination by filtration of the chromium residue        through resins;    -   h) concentration, cooling and drying of the gelatine separated;    -   i) selective regeneration of ion exchange filters;    -   j) concentration of the chromium salts obtained by diafiltration        and ion exchange filters regeneration, by evaporation in vacuo        with recovery of chromium salts and of water to be recycled.

The following examples concerning gelatines preparation and chromiumsalts and hydrolysing agent recovery on the basis of the claimedprocess, are conveyed by way of illustration, not of limitation of thepresent invention.

EXAMPLE 1 Acid Hydrolysis, Filtration and Desalination

A 200 l reactor was fed with shaving (10 kg) containing 56% moisture andapprox. 2% trivalent chromium, with 20–30% by wt. citric acid solution(6 kg) and distilled water (34 kg). Shaving was allowed to hydrate atroom temperature for some hours and stirred by an anchor stirrer. Thereaction mass was heated to 20° C. with continued stirring by an anchorstirrer and slight air bubbling to favour mixing. Hydrolysis was startedby steam modulation in the reactor jacket. After 2-hr heating to 80–90°C., hydrolysis of the shaving was obtained. The resulting product wasdiluted with distilled water in a ratio equal to 1:1 by wt. to give asolution (90 l) at 60° C., with 9% glue weight.

Filtration, which was carried out with 100 micron felt vessel mechanicalbag filter instead of a centrifuge, had been preceded by a first roughfiltration using a 400 micron filtering bag and a further dilutionthermostated at 50° C. in a batch reactor. Filtration gave a 100 micronhydrolysate solution and approx. 3–4% unreacted residue (on a drybasis).

Hydrolysis yield referred to shaving as it is: 83% by wt.

A portion of gelatine obtained by acid hydrolysis and filtration wasdesalted by causing it to pass in two columns containing weak anionresin and strong cation resin (150 ml each). In particular, gelatine(380 ml) was diluted with distilled water (1:1) and caused to pass intwo columns containing anion resin A100 and cation resin C150 (150 ml),regenerated and preheated to 180° C. with water. This operation wasperformed with diluted gelatine at 50° C. at a specific rate of 5 BV(Bed Volume). The resulting solution was concentrated in vacuo.

Desalination gave a gelatine solution exhibiting:

glue weight: 16%; sp. gr.: 1.034 at 40° C.; viscosity: 115.4 mpoise at40° C.

Solution drying gave a gelatine exhibiting the followingcharacteristics:

Bloom: 421; viscosity: 127 mpoise; citric acid: n.d.; Cr(III): 0.15% bywt.; moisture content: 17%; ashes content at 560° C.: 1.1%.

EXAMPLE 2 Acid Hydrolysis, Filtration and Desalination

A laboratory flask was fed with shaving (50 g) containing 56% moistureand approx. 2% trivalent chromium, and with 9 to 10% lactic acidsolution (400 ml). Once the mass had been hydrated for some hours atroom temperature under stirring by an anchor stirrer, it was hydrolysed(96%) at approx. 90° C. for 30 min., then diluted with distilled water(1:1) at room temperature and filtered through drymad cloth. Thesolution was allowed to percolate into a column containing mixed bedresins, preheated with water to 80° C. The solution was concentrated anddried to give a gelatine exhibiting the following characteristics:

Bloom: 370; Cr(III): 0.2% by wt.; ashes content: 1.5% by wt.; moisturecontent: 10% by wt.

EXAMPLE 3 Gelatine Dialysis, Concentration and Drying

The gelatine solution obtained by filtration as per example 1 wascollected in a tank and thermostated at 50° C. The solution was dialysedby an ultrafiltration unit with a membrane with cut-off of approx 6000to separate the gelatine from the hydrolysing agent and chromium, oncethe retentate (gelatine) volume had been reduced by 50%, and osmosizedwater at 50° C. had been added portionwise in a 1:2 ratio by vol. tofavour the dialysis of citric acid and of chromium. Finally, theretentate was further reduced.

Dialysis gave:

a gelatine with a citric acid residue of 0.2% by wt. and a chromiumresidue of 0.01% by wt.;

a permeate with a citric acid content of approx. 0.2% by wt. and achromium content of 0.005% by wt.

The gelatine solution obtained by dialysis was concentrated to give asemi-firm gelatine with 12.5% glue weight as well as distilled waterthat was recovered.

The semi-firm gelatine was solidified, ground and dried. Concentrationgave a gelatine exhibiting the following characteristics:

Yield referred to hydrolysed shaving: 30% by wt.; Bloom: 324; moisturecontent: 3%; viscosity (Ostwald): 177 mpoise at 12.5%; citric acid: 5%by wt.; Cr(III): 0.2% by wt.; ashes content at 560° C.: 2.1%.

EXAMPLE 4 Citric Acid Diafiltration

The permeate obtained by gelatine dialysis as per example 3 wasconcentrated by means of a nanofiltration unit with membrane withcut-offs of 200 to 300, to give a permeate free from chromium, but witha small amount of recovered citric acid. Said amount is small becausethe process is batch type; instead a continuous process understeady-state conditions would give a higher amount of recovered citricacid. Diafiltration gave:

a permeate free from chromium and with a citric acid content of 0.02% bywt.;

a retentate with a citric acid content of 1.4% by wt. and a chromiumcontent of 0.039% by wt.

The permeate obtained by diafiltration was concentrated by a reverseosmosis unit. In particular, the following was obtained:

a retentate with citric acid content of 0.3% by wt.;

osmosized water with a citric acid residue of 30 ppm.

EXAMPLE 5 Acid Hydrolysis, Filtration and Dialysis

A laboratory flask was fed with shaving (50 g) containing 56% moistureand approx. 2% trivalent chromium, and with a 4–5% citric acid solution(600 ml). The mass was hydrolysed (99%) at approx. 50° C. for 30 hrs.under stirring by an anchor stirrer, diluted with distilled water (1:1)at room temperature and filtered through drymad cloth. The filteredsolution was dialysed by ultrafiltration with dialysis cell withaddition of distilled water (3 l) at 50° C. The solution wasconcentrated and dried to give a gelatine exhibiting the followingcharacteristics:

Bloom: approx. 370; Cr(III): 0.4% by wt.; ashes content: 2% by wt.;moisture content: 6% by wt.

EXAMPLE 6 Selective Regeneration of Resins Columns

Once the gelatine sample had been desalted as per Example 1, the anionresin column was regenerated with a solution consisting of 30% NaOH anddistilled water heated to 60° C., in a 1:5 ratio by vol. The column waswashed with low-flow-rate distilled water and then with high-flow-ratedistilled water. Eluates were collected to obtain a concentrated eluate(core) rich in trivalent chromium.

The head and tail, which consisted of aqueous eluate and, respectively,of an eluate poor in Cr, were combined to give the mother liquid whichmay be reused to regenerate the anion column in the successive steps:

head+tail: 40% by vol.; Cr content: 0.04%, NaOH content: 0.7%.

The “core” is the concentrate that may be utilised by salcromomanufacturers.

Core: 10% by vol.; Cr content: 0.2%, NaOH content: 0.3%.

EXAMPLE 7 Acid Hydrolysis, Filtration, Dialysis, Desalination,Diaflltration and Selective Regeneration

A 200 l reactor was fed with shaving (10 kg) containing 56% moisture andapprox. 2% trivalent chromium, with 20–30% by wt. citric acid solution(6 kg) and distilled water (34 kg). Shaving was allowed to hydrate atroom temperature for some hours and stirred by means of an anchorstirrer. The reaction mass was heated to 20° C. with continued stirringby an anchor stirrer and slight air bubbling to favour mixing.Hydrolysis was started by steam modulation in the reactor jacket. After2-hr heating to 80–90° C., hydrolysis of the shaving was obtained. Theresulting product was diluted with distilled water in a ratio equal to1:1 by wt. to give a solution (90 l) at 60° C., with 9% glue weight.

Filtration, which was carried out with 100 micron felt vessel mechanicalbag filter and not with a centrifuge, had been preceded by a first roughfiltration using a 400 micron filtering bag, and a further dilutionthermostatted at 50° C. in a batch reactor. Filtration gave a 100 micronhydrolysate solution and approx. 3–4% unreacted residue (on a drybasis).

Hydrolysis yield referred to shaving as it is: 83% by wt.

The gelatine solution resulting from filtration was collected in a tankand thermostated at 50° C. The solution was dialysed by anultrafiltration unit with a membrane with cut-off of approx 6000 toseparate the gelatine from the hydrolysis agent and chromium, once theretentate (gelatine) volume had been reduced by approx. 50%, andosmosized water at 50° C. had been added portionwise in a 1:2 ratio byvol. to favour the dialysis of citric acid and of chromium. Finally, theretentate was further reduced.

Dialysis gave:

a gelatine with a citric acid residue of 0.2% by wt. and a chromiumresidue of 0.01% by wt.;

a permeate with a citric acid content of approx. 0.2% by wt. and achromium content of 0.005% by wt.

Some gelatine solution obtained by dialysis was desalted by causing itto pass in two columns containing weak anion resin and strong cationresin (150 ml each). In particular, gelatine (400 ml) was diluted withdistilled water (1:1) and caused to pass in two columns containing anionresin A100 and cation resin C150 (150 ml), regenerated and preheated to80° C. with water. This operation was performed with diluted gelatine at50° C. at a specific rate of 5 BV (Bed Volume). The resulting solutionwas concentrated in vacuo.

Solution drying gave a gelatine exhibiting the followingcharacteristics:

Bloom: 436; viscosity: 153 mpoise; citric acid: n.d.; Cr(III): 0.12% bywt.; moisture content: 17%; ashes content at 560° C.: 1.5%.

The permeate obtained by gelatine dialysis was concentrated by means ofa nanofiltration unit with membrane with a cut-off of 200 to 300, togive a permeate free from chromium, but with a small amount of recoveredcitric acid. Said amount is small because the process is batch type;instead a continuous process under steady-state conditions would give ahigher amount of recovered citric acid.

Diafiltration gave:

a permeate free from chromium and with a citric acid content of 0.02% bywt.;

a retentate with a citric acid content of 1.4% by wt. and a chromiumcontent of 0.039% by wt.

The permeate obtained by diafiltration was concentrated by a reverseosmosis unit. In particular, the following was obtained:

a retentate with a citric acid content of 0.3% by wt.;

osmosized water with a citric acid residue of 30 ppm.

Once the gelatine sample had been desalted, the anion resin column wasregenerated with a solution consisting of 30% NaOH and distilled waterheated to 60° C., in a 1:5 ratio by vol. The column was washed withlow-flow-rate distilled water and then with high-flow-rate distilledwater. Eluates were collected to obtain a concentrated eluate (core)rich in trivalent chromium.

The head and tail, which consisted of aqueous eluate and, respectively,of an eluate poor in Cr, were combined to give the mother liquid whichmay be reused to regenerate the anion column in the successive steps:

head+tail: 40% by vol.; Cr content: 0.04%, NaOH content: 0.7%.

The “core” is the concentrate that may be utilised by salcromomanufacturers.

Core: 10% by vol.; Cr content: 0.2%, NaOH content: 0.3%.

EXAMPLE 8 Acid Hydrolysis with Lactic and Formic Acids, Filtration andDialysis

A laboratory flask was fed with 50 g of skin shaving containing 56%moisture and approx. 1.2% trivalent chromium, 350 ml of a formic acidsolution at 9–10% and 50 ml lactic acid solution at 9%. After hydrationfor 1 hour, at room temperature under stirring by a anchor stirrer, themass had been hydrolysed at 80% at approx. 90° C. for 30 min. The massobtained after hydrolysis had been diluted 1:1 with distilled water atroom temperature and then filtrated through drymad-type canvas; then thefiltrated solution had been dialysed for ultrafiltration with dialysiscell adding approx. 2 lt. of distilled water at 50° C.; finally, thesolution had been percolated through a column containing mixed bed-resinpre-heated with water at 80° C. After solution concentration and drying,the gelatine obtained had the following characteristics:

Bloom 360; Chrome(III) 0.2% wt./wt.; ashes 1.55% wt./wt.; moisture 10%wt./wt.

EXAMPLE 9 Acid Hydrolysis with Citric and Sulphuric Acids, Filtrationand Desalination.

A laboratory flask was fed with 50 g of skin shaving, containing 41%moisture and approx. 2% trivalent chromium, 550 ml of sulphuric acidsolution at approx. 2.5% and 50 ml citric acid solution at approx. 6.5%.The mass had been hydrolysed at 85% at approx. 90° C. for 90 min, understirring by a anchor stirrer. The mass obtained after hydrolysis hadbeen diluted 1:1 with distilled water at room temperature and thenfiltrated through drymad-type canvas; then the filtrated solution hadbeen further diluted 1:1 and desalinated at 50° C. by a double steppercolation through two columns containing 150 ml each weak anionicresin and strong cationic resin pre-heated with water at 80° C.

After concentration and drying of the solution, the gelatine obtainedhad the following characteristics:

Bloom 336; Chrome (III) 0.15% wt./wt.; ashes 1.1% wt./wt.; moisture 10%wt./wt.

EXAMPLE 10 Hydrolysis With Edta Disodium Salt and Sulphuric Acids,Filtration and Desalination.

A laboratory flask was fed with 50 g of shaving, containing 41% moistureand approx. 16% trivalent chromium, 350 ml of a sulphuric acid solutionat approx. 2.5% and 350 ml salt disodium EDTA solution at approx. 2.5%.The mass had been hydrolysed at 80% at approx. 90° C. for 60 min, understirring by a anchor stirrer. The mass obtained after hydrolysis hadbeen diluted 1:1 with distilled water at room temperature and thenfiltrated through drymad-type canvas; then the filtrated solution hadbeen further diluted 1:1 and desalinated at 50° C. by a double steppercolation through two columns containing 150 ml each weak anionicresin and strong cationic resin pre-heated with water at 80° C.

After concentration and drying of the solution, the gelatine obtainedhad the following characteristics:

Bloom 320; Chrome (III) 0.17% wt./wt.; ashes 1.2% wt./wt.; moisture 13%wt./wt.

The claimed process entirely complies with the aforementioned objects ofthe present invention, i.e. the development of industrial processes,capable of recovering—from tanned hides and skins shaving—by-products(collagen gelatine and chromium) that may be recycled to and reused inindustrial plants, thereby minimising the problem arising from theirdisposal; the obtainment of choice products of high economic value, forsuccessive industrial applications; the development of a process havingno environmental impact and, therefore, envisaging a complete reus ofits by-products (hydrolysing agents, regenerants, and wastewaters) andnot generating polluting gas emissions.

In this respect, it is to b noted that the envisaged and essential acidhydrolysis is very fast and gives a hydrolysate in a yield of approx.80°/ in respect of shaving as it is, without any alkaline treatment.Finally, the hydrolysis gives a gelatine of satisfactory quality and, inany case, exhibiting a Bloom's resistance not less than 300, and doesnot generate gaseous by-products. Non-hydrolysed tanned hides and skinsshaving products may be recycled for further hydrolysis. Said step maybe repeated several times until complete, or anyhow, exhaustivehydrolysis of the starting material without detriment to the gelatinequalitative yields. The successive hydrolysis cycles, in fact, givetechnical-grade gelatines exhibiting constant qualitative chacteristics.

The hydrolysate consisting of gelatine, hydrolysing agent and chromiumsalts is separated in successive separation steps to give three mainproducts: gelatine, regenerated hydrolysing agent and chromium salts insolution.

All products are further processed and recovered: in particular, thegelatine is marketed; the chromium salts are utilised by saicromomanufacturers for tanning and, therefore, is reused industrially; thehydrolysing agent, the ion-exchange-columns regenerant and water arecontinuously recycled.

It is of major importance that the process never uses polluting agentsand does not generate liquid or gaseous emissions: therefore, it isecofriendly. Only gelatine drying brings about a low water loss. Afurther, but not secondary feature related to the environmental impactof the process is that—unlike the processes for protein hydrolysatesproduction by alkaline hydrolysis—the process degradation of the amidicgroup does not produce ammonia.

Numerous variations and modifications may be effected without departingfrom the spirit and scope of the novel concept of the invention.Therefore, the claimed process may be modified and perfected by thoseskilled in the art, according to the technical knowledge and experiencegained in the sector as well as to the normal evolution of the state ofthe art.

1. Process for gelatine production and chromium salts recovery from tanned hides and skins shaving products, comprising at least by the following steps: organic acid hydrolysis at temperatures to 100° C., excluding room temperature; extraction by filtration of the raw gelatine obtained after hydrolysis; technical-grade gelatine and chromium salts separation by desalination.
 2. The process as claimed in claim 1 wherein the organic acid hydrolysis is characterised by: the use of organic acids selected from the group consisting selected from the group consisting of monocarboxylic, polycarboxylic, hydroxy acids, the salts and mixtures thereof; a ratio of 10 to 80% wt./wt. of said acids to the shaving products with an average moisture content of approx. 55%; a water weight ratio ranging from 4 to 10 times the weight of the shaving products with an average moisture content of approx. 55% mass heating to a temperature ranging from 50° C. to 100° C.
 3. The process as claimed in claim 1 and 2, wherein the organic acids are combined with mineral acids, in a ratio of 5 to 20% wt./wt. of said mineral acids to the shaving products with an average moisture content of approx. 55%.
 4. The process as claimed in any of claims 1 to 3 wherein the organic acids are formic, lactic, citric, EDTA, tartaric acids, the salts and mixtures thereof.
 5. The process as claimed in any of claims 1 to 4, wherein the mineral acids are selected from the group consisting of sulphuric and phosphoric acids.
 6. The process as claimed in claim 2, wherein the time of mass residence under the selected temperature conditions is ranging from 0.5 to 30 hrs.
 7. The process as claimed in claim 1, wherein the raw gelatine extraction is characterised by mass filtration after dilution.
 8. The process as claimed in claim 7, wherein the filtration for raw gelatine extraction is obtained using mechanical filtering means, selected from centrifugal separators, drum filters, bag filters, filter press, rotational separators.
 9. The process as claimed in any of claims 1 to 8 wherein the acid hydrolysis and filtration are repeated until complete gelatine extraction.
 10. The process as claimed in claim 1, wherein the gelatine and chromium salts separation is characterised by on or more desalinations over ion, cation and anion or mixed-bed, exchange resins selective for trivalent Cr.
 11. The process as claimed in any of claims 1 to 10, comprising the following further steps: gelatine and chromium salts separation by dialysis after filtration; chromium salts separation by diafiltration, after dialysis, with additional hydrolysing agent recovery and recycling.
 12. The process as claimed in claim 11, wherein dialysis is performed across porous membranes with molecular sieve of 1,000 to 30,000 dalton.
 13. The process as claimed in claim 11, wherein diafiltration is performed through porous membranes with molecular sieve of 200 to 500 dalton.
 14. The process as claimed in any of claims 1 to 13, comprising the following further step: ion exchange filters selective regeneration for total chromium recovery.
 15. The process as claimed in claim 14, wherein the ion exchange resins selective regeneration is obtained with acid and alkaline regenerants and successive washings and gives a head poor in regenerant and chromium salts, a core poor in regenerant, but rich in chromium salts, which forms the concentrated phase of chromium recovery, and a tail rich in regenerant and poor in chromium salts.
 16. The process as claimed in claim 15, wherein the head poor in regenerant and chromium salts and the tail rich in regenerant and poor in chromium salts are combined to recover the regenerant to be reused in the successive ion exchange columns regenerations.
 17. The process as claimed in any of claims 1 to 16, comprising all the following steps: organic acid hydrolysis at temperatures to 100° C., excluding room temperature; extraction by filtration of the raw gelatine obtained after acid hydrolysis; gelatine and chromium salts separation by dialysis after filtration; technical-grade gelatine and chromium salts separation by desalination after dialysis; ion exchange filters selective regeneration for total chromium recovery; chromium salts separation by diafiltration, after dialysis, with the addition hydrolysing agent recovery and recycling.
 18. The process as claimed in any preceding claims, wherein the gelatine solutions obtained by desalination and/or dialysis are recovered and concentrated.
 19. The process as claimed in any preceding claims, wherein the chromium salts solutions obtained by desalination and/or diafiltration and/or ion exchange resins selective regeneration, are recovered and concentrated.
 20. The process as claimed in any preceding claims, wherein the phases containing the hydrolysing agent obtained by desalination and/or diafiltration are recovered and recycled.
 21. The process as claimed in any preceding claims, wherein the water recovered during gelatine and chromium salts concentration is recycled. 